Re: [PATCH net 2/2] net: dsa: Avoid cross-chip syncing of VLAN filtering

[Vladimir Oltean <olteanv@gmail.com>]

On Mon, Jan 24, 2022 at 10:09:44PM +0100, Tobias Waldekranz wrote:
> Changes to VLAN filtering are not applicable to cross-chip
> notifications.

Yes, it seems so. In a cross-chip setup, ports will individually leave
the bridge, leaving every switch a chance to unset VLAN filtering.
We have this check in dsa_port_vlan_filtering(), so it's easy to forget
that the function is called more times than actually needed:

	if (dsa_port_is_vlan_filtering(dp) == vlan_filtering)
		return 0;

Sorry.

> On a system like this:
> 
> .-----.   .-----.   .-----.
> | sw1 +---+ sw2 +---+ sw3 |
> '-1-2-'   '-1-2-'   '-1-2-'
> 
> Before this change, upon sw1p1 leaving a bridge, a call to
> dsa_port_vlan_filtering would also be made to sw2p1 and sw3p1.
> 
> In this scenario:
> 
> .---------.   .-----.   .-----.
> |   sw1   +---+ sw2 +---+ sw3 |
> '-1-2-3-4-'   '-1-2-'   '-1-2-'
> 
> When sw1p4 would leave a bridge, dsa_port_vlan_filtering would be
> called for sw2 and sw3 with a non-existing port - leading to array
> out-of-bounds accesses and crashes on mv88e6xxx.
> 
> Fixes: d371b7c92d19 ("net: dsa: Unset vlan_filtering when ports leave the bridge")
> Signed-off-by: Tobias Waldekranz <tobias@waldekranz.com>
> ---
>  net/dsa/switch.c | 8 +++++---
>  1 file changed, 5 insertions(+), 3 deletions(-)
> 
> diff --git a/net/dsa/switch.c b/net/dsa/switch.c
> index 9f9b70d6070a..517cc83d13cc 100644
> --- a/net/dsa/switch.c
> +++ b/net/dsa/switch.c
> @@ -180,9 +180,11 @@ static int dsa_switch_bridge_leave(struct dsa_switch *ds,
>  						info->sw_index, info->port,
>  						info->bridge);
>  
> -	err = dsa_switch_sync_vlan_filtering(ds, info);
> -	if (err)
> -		return err;
> +	if (ds->dst->index == info->tree_index && ds->index == info->sw_index) {
> +		err = dsa_switch_sync_vlan_filtering(ds, info);
> +		if (err)
> +			return err;
> +	}

As net-next material, we could probably move this call to
dsa_port_switchdev_unsync_attrs() where there's even a comment that
references it, and do away with the targeted switch check.

>  
>  	return dsa_tag_8021q_bridge_leave(ds, info);
>  }
> -- 
> 2.25.1
> 

Reviewed-by: Vladimir Oltean <olteanv@gmail.com>